BRUSSELS/LONDON, Nov 1 (Reuters) - British Prime MinisterDavid Cameron came under pressure to act tough on the EuropeanUnion budget and France threatened to use its veto, signalling adivisive start to bargaining over the 1 trillion euro ($1.3trillion) long-term spending plan.

Wednesday's warning from Paris echoed a similar threat fromDenmark last week, while in London Cameron suffered ahumiliating defeat in parliament by Conservative rebelsdetermined to push him to take a hard line over Europe, an issuethat has long divided his party.

Although the British parliamentary vote is non-binding,mutinous Conservatives said it added force to their demand thatCameron should end his backing for a freeze in EU spending anddemand outright cuts.

The French ultimatum was prompted by a proposal to trim farmsubsidies - jealously guarded by Paris as the top recipient ofsuch payments - as part of a compromise from the Cypriot EUpresidency to cut the 2014-2020 budget by more than 50 billioneuros.

Even after the proposed cut, agriculture would remain thelargest spending area, with deeper cuts pencilled in forinfrastructure investment in the bloc's poorest regions as wellas research.

"We oppose the proposed reduction," French European AffairsMinister Bernard Cazeneuve said in a statement.

"France would not support a multi-annual budget that doesnot maintain the funds of the common agricultural policy."

The backlash was also a warning not to cut the proposed farmbudget further, after Cyprus said much deeper reductions thanthose outlined so far would be needed to clinch a deal.

Despite support from Ireland and Austria, France's positionputs it on a collision course with Germany, Britain and othernet contributors looking to slash overall spending by 100-200billion euros.

EU diplomats have warned privately that further cuts arelikely to hit agriculture hardest. A Franco-German deal tomaintain the nominal level of farm spending served as the basisfor agreement on the last long-term EU budget for 2007-2013.

But German deputy foreign minister Michael Link hinted Pariscould be fighting a losing battle this time, saying Berlin wouldcontinue to press for deeper overall cuts as part of a "modernbudget" that prioritises economic growth and competitiveness.

"We don't think the presidency has found the right emphasisyet," Link said.

"CUTTING OUR CLOTH"

The rebels won the British parliamentary vote on Wednesdayevening by 307 to 294, a majority of 13, after they receivedsupport from the Labour Party, a generally pro-European groupaccused by Cameron of "rank opportunism" because it had approvedEU budget increases while in office.

"This is a time for Brussels to listen to the British peopleand do what we are all doing, and that is cutting our cloth,"Conservative lawmaker Mark Pritchard, one of the revolt'sleaders, told Sky News.

Rebels said the vote could strengthen Cameron's position atbudget talks in Brussels next month because he will be able tosay his hands are tied by the British parliament.

But other Conservatives say Cameron will be weakened afterhis first significant defeat in parliament since taking power in2010.

Conservative rebels had urged the prime minister to insiston cuts to EU spending to reflect the bleak economic landscapeacross much of Europe.

"This government is taking the toughest line in these budgetnegotiations of any government since we joined the EuropeanUnion," Cameron told parliament ahead of the vote.

"At best we would like it cut, at worst frozen, and I'mquite prepared to use the veto if we don't get a deal that'sgood for Britain," he said.

EU leaders will try to resolve their differences at a summitin Brussels on Nov. 22-23, which is likely to involve long daysand late nights of bitter horse trading.

With agriculture and regional development spending togetheraccounting for about three-quarters of the total budget, leaderslooking to limit their EU contributions may ultimately be forcedinto a straight choice between the two.

Poland, like most poorer Eastern member states, receives farless in EU farm support than in regional development funds,credited with helping it avoid a recession.

Making the case for maintaining development spending, PolishEurope Minister Piotr Serafin said the benefits would be feltacross the EU -- an argument that may sway Berlin and others inthe final reckoning.

"Poland is a country that makes particular good use ofstructural money and has a major impact on the region'seconomy," he told Reuters in an interview.

"Poland generates growth in other EU members, it generatesextra GDP, it adds to the overall welfare of the EU, so it's agood investment."